If someone makes an extraordinary claim, ask for extraordinary evidence.

Is it true humans were in the Americas more than 100,000 years ago? - Sarah, Toronto

It’s true a study to that effect was recently published in Nature. It describes 130,000-year-old mastodon bones in San Diego, Calif., that appear to have been snapped by human hands, perhaps to make tools or extract the tasty bone marrow. The very heavy rocks found alongside them could be ancient anvils.

To use a scientific term, these findings are pretty wack. A large body of evidence shows the first humans in the Americas crossed the ice between present-day Russia to Alaska between 15,000 and 13,000 years ago, not before.

Homo sapiens were still in Africa 130,000 years ago. But human relatives with whom we share ancient common ancestors had made it to Europe and Asia.So it’s not insane to suppose they could have crossed into North America. But I’m very, very skeptical. Extraordinary claims that go against scientific consensus require extraordinary evidence.

Their iconoclasm might be subtle. They often hold appointments at prestigious universities and publish in peer-reviewed journals; though usually the same obscure ones over and over.

William Davis, a.k.a. the Wheat Belly guy, believes bread is the source of all our ills. His dairy counterpart, Neal Barnhard, is on a crusade against a “dangerous” and “addictive” public-health menace: cheese. Frederick vom Saal and a few of his close colleagues at the University of Missouri are convinced consuming trace amounts of BPA poses an imminent danger to health, a position regulatory agencies and toxicologists have refuted.

Sometimes crusaders are proven right. Paradigms get upended. But that only happens after the discovery of more, better, and independent evidence: Not from crusaders’ chums.